A piezoelectric/electrostrictive actuator has such an advantage that a displacement can be accurately controlled in a submicron order. Particularly, a piezoelectric/electrostrictive actuator using a sintered body of piezoelectric/electrostrictive ceramics as a piezoelectric/electrostrictive body can accurately control a displacement, and also has advantages such as high electromechanical conversion efficiency, a large generation force, a high response speed, high durability and less power consumption. Therefore, the piezoelectric/electrostrictive actuator using the sintered body of piezoelectric/electrostrictive ceramics as the piezoelectric/electrostrictive body is employed as a head of an inkjet printer, an injector of a diesel engine and so on utilizing these advantages.
As the sintered body of piezoelectric/electrostrictive ceramics for a piezoelectric/electrostrictive actuator, a lead zirconate titanate (hereinafter referred to as “PZT”)-based leaded piezoelectric/electrostrictive material has hitherto been used. However, ever since an influence of lead from a sintered body on the global environment came to be strongly feared, it has also been studied to use a lead-free piezoelectric/electrostrictive material such as a sodium bismuth titanate (hereinafter referred to as “BNT”)-based material.
In a BNT-based lead-free piezoelectric/electrostrictive material, there was made a trial of increasing an electric field-induced strain, which is important for a piezoelectric/electrostrictive actuator, by solid-dissolving bismuth potassium titanate (hereinafter referred to as “BKT”) or barium titanate (hereinafter referred to as “BT”) in BNT. However, it is difficult to obtain a large electric field-induced strain, which is equivalent to that of a PZT-based leaded piezoelectric/electrostrictive material, only by the above method.
Therefore, trials for obtaining a larger electric field-induced strain by introducing defects into a crystal have been made.
For example, Non-Patent Document 1 describes that a large electric field-induced strain is obtained by introducing defects into a single crystal of BNT-BKT-BT, which is a solid solution of BNT, BKT and BT.
Patent Documents 1 and 2 describe that a large electric field-induced strain is obtained by substituting a portion of constituent elements with a donor or an acceptor and introducing defects having the same symmetry as that of a crystal into a single crystal or ceramics through an aging treatment for 5 days to 3 months.